This invention relates generally to diesel engines that have diesel particulate filters for treating exhaust gases passing through their exhaust systems. More particularly, the invention relates to engine systems and methods for forcing regeneration of such filters.
A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine. The amount and the timing of engine fueling are two functions that are controlled by an engine control system. A typical diesel engine that comprises fuel injectors for injecting fuel into the engine cylinders under control of an engine control system controls both the duration and the timing of each fuel injection to set both the amount and the timing of engine fueling. In a turbocharged diesel engine, the electronic engine control system also exercises control over turbocharger boost.
An exhaust system of a diesel engine that comprises a diesel particulate filter (DPF) is capable of physically trapping diesel particulate matter (DPM) in exhaust gas passing through the exhaust system from the engine. This prevents significant amounts of DPM from entering the atmosphere.
DPM includes soot or carbon, the soluble organic fraction (SOF), and ash (i.e. lube oil additives etc.). The trapping of those constituents by a DPF prevents what is sometimes seen as black smoke billowing from a vehicle""s exhaust pipe. The organic constituents of trapped DPM, i.e. carbon and SOF, are oxidized within the DPF at appropriate times and under appropriate conditions to form CO2 and H2O, which can then pass through and exit the exhaust pipe to atmosphere. The ash collects within the DPF over time, progressively aging the DPF by gradually reducing its trapping efficiency.
One type of known DPF is marketed by Johnson Matthey Company under the trade name xe2x80x9cContinuously Regenerating Trapxe2x80x9d or (CRT(trademark)). An oxidation catalyst is disposed upstream of the DPF. The oxidation catalyst oxidizes hydrocarbons (HC) to CO2 and H2O and converts NO to NO2. The NO2 oxidizes carbon trapped in the DPF. While O2 could be used to oxidize DPM, the high temperatures for accomplishing oxidation make O2 rather impractical for treating diesel engine exhaust without the aid of still another catalyst such as cerium-oxide (CeO2), and as one might expect, the inclusion of a second catalyst would make such an exhaust treatment system even more expensive.
Another type of known DPF is marketed by Englehard Corporation under the trade name DPX(trademark). It is sometimes referred to as a Catalyzed Soot Filter (or CSF). The Engelhard CSF has an additional CeO2 catalyst that eliminates the need for an upstream oxidation catalyst, which in turn reduces the overall size of a DPF and avoids the greater pressure drops present in a two-substrate DPF like a CRT(trademark) filter. In both types of DPF, the oxidation catalyst oxidizes hydrocarbons (HC) and converts NO to NO2, with the NO2 then being used to oxidize the trapped carbon.
The rate at which trapped carbon is oxidized to CO2 is controlled not only by the concentration of NO2 or O2 but also by temperature. Specifically, there are three important temperature parameters for a DPF.
The first is the oxidation catalyst""s xe2x80x9clight offxe2x80x9d temperature, below which catalyst activity is too low to oxidize HC. That temperature is typically around 180-200xc2x0 C.
The second controls the conversion of NO to NO2. This NO conversion temperature spans a range of temperatures having both a lower bound and an upper bound, which are defined as the minimum temperature and the maximum temperature at which 40% or greater NO conversion is achieved. The conversion temperature window defined by those two bounds extends from approximately 250xc2x0 C. to approximately 450xc2x0 C.
The third temperature parameter is related to the rate at which carbon is oxidized in the filter. Reference sources in relevant literature call that temperature the xe2x80x9cBalance Point Temperaturexe2x80x9d (or BPT). It is the temperature at which the rate of oxidation of particulate, also sometimes referred to as the rate of DPF regeneration, is equal to the rate of accumulation of particulate. The BPT is one of the parameters that is especially important in determining the ability of a DPF to enable a diesel engine to meet expected tailpipe emissions laws and/or regulations.
Typically, a diesel engine runs relatively lean and relatively cool compared to a gasoline engine. That factor makes natural achievement of BPT problematic. Therefore, a manufacturer of a DPF for a diesel engine should strive for a design that minimizes BPT, and a diesel engine manufacturer should strive to develop engine control strategies for raising the exhaust gas temperature to temperatures in excess of BPT whenever the amount of trapped particulates exceeds some threshold that has been predetermined in a suitably appropriate manner, such as by experimentation. Using an engine control to raise exhaust gas temperature in this way is called forced regeneration.
Investigation of several methods for initiating a forced regeneration of a DPF has disclosed that retarding the start of main fuel injections seems to be the most effective way to elevate exhaust gas temperature. That method is able to increase the exhaust gas temperature sufficiently to elevate the catalyst""s temperature above catalyst xe2x80x9clight offxe2x80x9d temperature and provide excess HC that can be oxidized by the catalyst. Such HC oxidation provides the necessary heat to raise the temperature in the DPF above the BPT.
The method has been validated in a motor vehicle powered by a diesel engine whose exhaust system has a DPF. The DPF was loaded with soot, and regeneration was forced at low idle, 30 mph, 60 mph and high idle driving conditions. It was discovered that complete DPF regeneration may not always occur, as evidenced by the incomplete removal of all accumulated soot. Although a full understanding of that phenomenon has not yet been attained, the method does offer promise for eventual commercialization.
The present invention relates to engine systems and methods for accomplishing forced regeneration of DPF""s, preferably by retarding timing of engine fueling to create suitable exhaust gas temperatures.
A presently preferred embodiment of the invention disclosed herein comprises several sub-system models, including an engine emissions model, a DPM oxidation model, a DPM accumulation model, and an ash accumulation model. Data for various parameters relating to engine and DPF operation are processed through the models, and results are used to initiate and terminate forced regenerations via regeneration initiation/termination logic. The timing and the duration of a forced regeneration are thereby controlled. Examples of data processed by an engine control system processor for accomplishing this objective include pressure, temperature and O2 concentration data relevant to the DPF.
The forced regeneration process is itself conducted according to an algorithm that processes certain data to adjust both engine fueling and the timing of engine fueling to elevate exhaust gas temperature to a range sufficient to exceed the BPT of the DPF while at the same time striving for transparency of the process to the manner in which the motor vehicle is being driven so that the driver of the vehicle will not perceive that forced regeneration is occurring. The invention inherently accounts for altitude and ambient temperature effects, and it also accounts for DPF aging through use of the ash accumulation model. If a diesel engine has a turbocharger that provides boost, the invention also makes certain adjustments in control of the turbocharger to minimize effects of the elevated exhaust gas temperature on boost as forced regeneration proceeds.
Accordingly, several generic aspects of the present invention relate to a method of imposing a forced regeneration cycle on a DPF that treats exhaust gas passing through an exhaust system of a diesel engine to force regeneration of the DPF.
According to one of these several generic aspects, data that represents engine speed, data that represents engine fueling, data that represents turbocharger boost, and data that represents exhaust gas recirculation (EGR) from the exhaust system back into the engine, are processed, while the engine is running, through an engine emissions model to yield values representing rates at which DPM from the engine is entering the exhaust system and values for NOX concentration in the exhaust gas. The values for NOX concentration in the exhaust gas, values representing concentration of O2 in the exhaust gas entering the DPF, and values representing temperature of exhaust gas entering the DPF are repeatedly processed through a DPM oxidation model to yield values of DPM oxidation rate data representing the rate at which DPM is being oxidized in the exhaust system. The values of DPM oxidation rate data and the values representing a rate at which DPM from the engine is entering the exhaust system are repeatedly processed through a DPM accumulation model to yield values of net DPM accumulation representing net accumulation of DPM in the DPF at various points of time while the engine is running. Accumulated engine running time is processed through an ash accumulation model to yield data representing ash accumulation in the DPF. The values of net DPM accumulation and the data representing ash accumulation are repeatedly processed through regeneration initiating/terminating logic for commanding a forced regeneration cycle when a result of the latter processing calls for initiation of forced regeneration of the DPF and for discontinuing the forced regeneration cycle when a subsequent result calls for termination of the forced regeneration cycle.
According to another of these several generic aspects, data that represents parameters useful in determining a rate at which DPM is accumulating in the DPF is repeatedly processed through a DPM accumulation model to yield values of DPM accumulation representing accumulation of DPM in the DPF at various points of time as the engine runs. The values of DPM accumulation and data that distinguishes DPM accumulation values calling for forced regeneration from those not calling for forced regeneration are also processed, and when a result of the latter processing discloses that a DPM accumulation value calls for forced regeneration of the DPF, forced regeneration is initiated by retarding the timing of engine fueling to elevate the exhaust gas temperature to a temperature for forcing regeneration. As the forced regeneration cycle progresses, baseline engine fueling data representing engine fueling at commencement of the forced regeneration cycle, engine speed data that represents engine speed, data representing light off temperature of catalytic material of the DPF, and data representing actual temperature of the catalytic material, are processed to yield adjusted timing values for timing of engine fueling and fueling modification values. Engine fueling data representing engine fueling in the absence of forced regeneration of the DPF and the fueling modification values are processed to yield adjusted fueling values. As the forced regeneration continues, the adjusted fueling values are used instead of the engine fueling data for fueling the engine, and the adjusted timing values are used for the timing of engine fueling.
According to still another of these several generic aspects, data that represents temperature of exhaust gas entering the DPF, data that represents exhaust gas flow entering the DPF, and data that utilizes both exhaust gas temperature and flow to distinguish a DPF that has trapped an amount of DPM calling for forced regeneration from a DPF that does not call for forced regeneration, are processed to yield result data that a) calls for forced regeneration when the data that represents temperature of exhaust gas entering the DPF and the data that represents exhaust gas flow entering the DPF disclose that the DPF has trapped an amount of DPM calling for forced regeneration, and b) calls for no forced regeneration when the data that represents temperature of exhaust gas entering the DPF and the data that represents exhaust gas flow entering the DPF disclose that the DPF does not call for regeneration. When the result data calls for forced regeneration of the DPF, forced regeneration is initiated by retarding the timing of engine fueling to elevate the exhaust gas temperature to a temperature for forcing regeneration of the DPF. As the forced regeneration cycle progresses, baseline engine fueling data representing engine fueling at commencement of the forced regeneration cycle, engine speed data that represents engine speed, data representing light off temperature of catalytic material of the DPF, and data representing actual temperature of the catalytic material, are processed to yield adjusted timing values for timing of engine fueling and fueling modification values. Engine fueling data representing engine fueling in the absence of forced regeneration of the DPF and the fueling modification values are processed to yield adjusted fueling values. As the forced regeneration cycle continues, the adjusted fueling values are used instead of the engine fueling data for fueling the engine, and the adjusted timing values are used for the timing of engine fueling.
According to yet another of these several generic aspects, data that represents a rate at which DPM from the engine is entering the exhaust system, data that represents a rate at which DPM is being oxidized in the exhaust system, and data that represents DPM trapping efficiency of the DPF, are processed to yield values representing net rate at which DPM is being trapped in the DPF at various points of times as the engine runs. The values representing net rate at which DPM is being trapped and data representing effective geometric size of DPM trapping medium in the DPF are processed to yield values representing DPM trapped in the DPF per unit of geometric size of the DPM trapping medium. The values representing DPM trapped in the DPF per unit of geometric size of the DPM trapping medium and data distinguishing values of DPM trapped in the DPF per unit of geometric size of the DPM trapping medium that call for forced regeneration from those that do not are also processed, and when a result of the latter processing discloses that a value of data representing DPM trapped in the DPF per unit of geometric size of the DPM trapping medium calls for regeneration, the engine is operated in an elevated temperature mode of operation that elevates the exhaust gas temperature to a temperature for forcing regeneration. When a subsequent result discloses that a value of data representing DPM trapped in the DPF per unit of geometric size of the DPM trapping medium does not call for regeneration, operation of the engine in the elevated temperature mode of operation is discontinued.
According to yet one more of these several generic aspects, data for a first set of engine operating parameters is processed is running to yield values representing amounts of accumulation of DPM in the DPF at various points of times as the engine runs, and data for a second set of engine operating parameters different from the first set of engine operating parameters is also processed to yield values representing amounts of accumulation of DPM in the DPF at various points of times as the engine runs. When the processing of data for one of the first and second sets of engine operating parameters discloses a value calling for regeneration, the engine is operated in a mode of operation for forcing regeneration, and when a value resulting from subsequent processing of data for the one set of engine operating parameters discloses an amount of accumulation of DPM in the DPF does not call for regeneration, that mode of engine operation is discontinued.
According to yet one more of these several generic aspects, both baseline engine fueling data representing engine fueling at commencement of the forced regeneration cycle and engine speed data that represents engine speed are repeatedly processed according to a map that correlates values representing various timings for engine fueling during the forced regeneration cycle with both values of baseline engine fueling and values of engine speed to yield timing values for the timing of engine fueling as the forced regeneration cycle progresses. Data representing light off temperature of catalytic material of the DPF and data representing actual temperature of the catalytic material are repeatedly processed as the forced regeneration cycle progresses, to yield adjustment values for adjusting the timing values. The adjustment values and the timing values are processed to yield adjusted timing values for the timing of engine fueling during the forced regeneration cycle. The adjusted timing values and the engine speed data are processed according to a map that correlates fueling modification values with both the adjusted timing values and values of engine speed to yield fueling modification values. Engine fueling data representing engine fueling in the absence of forced regeneration of the DPF and the fueling modification values are processed to yield adjusted fueling values. As the forced regeneration cycle continues, the adjusted fueling values are used instead of the engine fueling data for fueling the engine, and the adjusted timing values are used for the timing of engine fueling.
Another aspect of the invention relates to a method for developing DPM oxidation rate data representing the rate at which DPM in diesel engine exhaust gas is being oxidized during passage through an exhaust system of a diesel engine that includes a catalyzed diesel particulate filter that treats the exhaust gas. Data that represents parameters useful in determining the concentration of NOX in exhaust gas entering the exhaust system from the engine are repeatedly processed to yield NOX concentration data for NOX concentration in the exhaust gas. The a) NOX concentration data, b) data representing concentration of O2 in the exhaust gas entering the DPF, c) data representing temperature of exhaust gas entering the DPF, and d) data for developing DPM oxidation rate data from NOX concentration data, O2 concentration data, and exhaust gas temperature data, are repeatedly processed to yield values of DPM oxidation rate data representing the rate at which DPM is being oxidized in the exhaust system.
The invention relates to methods and to apparatus embodying the foregoing aspects.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.